Vitamin D: More than Just Bone Health

Vitamin D has long been regarded as the primary hormone of bone metabolism.  However, we now know it may have many other effects.  Researchers found that vitamin D can be used by multiple body tissues.  A recent review article entitled, Vitamin D: A Review on Its Effects on Muscle Strength, the Risk of Fall, and Frailty, provides important insight based on the results of new paths of research.  Currently, there is evidence that vitamin D may be a player in the “regulation of the immune system, the cardiovascular system, oncogenesis, and cognitive functions.”

Chronic obstructive pulmonary disease, cardiac insufficiency, cancer, and chronic kidney disease (CKD) are just a few of the chronic diseases that include loss of muscle mass and frailty.  Vitamin D is also associated with the same diseases.  Researchers performed a review of studies from January, 2000 through September 2014.  Specifically, they looked for articles related to “the effect of vitamin D on skeletal muscles and its clinical implications, especially frailty and the risk of fall.”

The body metabolizes vitamin D by way of the skin, liver and kidney.  Approximately 80-90% of vitamin D formation is a result of production in the skin from sun exposure.  This leaves only 10-20% to be sourced from dietary consumption.  Factors such as exposure to sunlight, use of sunscreen/sunblock as well as skin pigmentation and kidney function may play into how much vitamin D an individual will produce.  In the elderly, with decreased function of the kidney, dietary vitamin D becomes more crucial.  This is especially true for elderly frail patients who may also have decreased nutritional intake.

While vitamin D is common, the specific data “may vary depending on the population studied and regional and seasonal considerations.”  For example, a study in Argentina found the prevalence to range between 52%-87% depending on the latitude.  Another study of elderly Italian women found the average occurrence to be 51% in the 6 months of December–May period but only 17% in the June–November period.

Multiple studies revealed a “significant association between low levels of vitamin D and poor physical performance.”  One study found patients with vitamin D levels below 25 had “poor physical performance as assessed by the handgrip strength test and a short physical performance battery test” than patients with levels above 25.  Additionally, an even larger increase in function was noted from patients with vitamin D levels above 50.  These results are similar to other studies.  The superior strength of subjects with higher vitamin D levels is consistent in younger individuals as well.

However, it is interesting that the differences seem to decrease in old age.  One study of individuals over the age of 80 showed no significant relationship between vitamin D levels and physical performance despite 80% of the subjects having vitamin D insufficiency.  Researchers concluded that this is due to the overall decrease of vitamin D receptors that is observed in very old individuals.

Numerous studies have been conducted to evaluate vitamin D supplementation.  Overall, the results support a daily vitamin D regimen.  This was most marked in older patients with vitamin D insufficiency/deficiency.  In most cases, 1000IU daily was sufficient to manifest improvement in muscle function.  However, studies with large intermittent doses did not show significant improvement in muscle strength and in some cases showed no improvement at all.  It is suggested that the high intermittent doses do not “maintain high serum levels for a sustained period.”

In the past, the association between vitamin D insufficiency and increased risk of falls and fractures was due to the changes in bone itself.  The newer data shows that vitamin D affects the skeletal muscles themselves and increases strength and function.

One study of community-dwelling seniors supplemented with 800 IU vitamin D and calcium daily found a 27% reduction in falls at one year and 39% reduction in falls at 20 months.  Another study demonstrated “a 49% reduction of falls in elderly women from a geriatric ward supplemented with 800 IU per day of vitamin D.”

“Frailty” is becoming a popular term in geriatric medicine.  A clinical definition has been made in order to give clinical indicators that can be measured.  Most of these indicators revolve around locomotion and physical strength and include: unintentional weight loss, self-reported exhaustion, weakness (grip strength), slow walking speed, and low physical activity.  Therefore, it is reasonable to think that low levels of vitamin D could lead to frailty.

Researchers concluded: “Considering that vitamin D supplementation is safe and inexpensive, it is worthy to recommend vitamin D supplementation in patients at risk for falls, such as elderly patients, nursing home residents, frail patients with gait and balance and visual impairments, and patients with chronic diseases. These patients are most likely to have low levels of vitamin D and muscle loss/dysfunction, thus justifying supplementation independent of a putative effect on the prevention of falls.”

 

Reference:

¹ Vitamin D: a review on its effects on muscle strength, the risk of fall, and frailty. Halfon M1, Phan O1, Teta D1. Published in BioMed Research International.  2015 Apr 27.